Method for manufacturing a metal stencil

ABSTRACT

METHOD FOR MANUFACTURING A METAL STENCIL BY STARTING FROM A CYLINDRICAL METAL MATRIX HAVING ON ITS SURFACE A PATTERN OF INSULATING MATERIAL; A THIN METAL WIRE IS TIGHTLY WOUND UPON SAID MATRIX, AFTER WHICH A LAYER OF METAL IS DEPOSITED UPON THE MATRIX, WHEREUPON THE LAYER IS REMOVED FROM THE MATRIX.   D R A W I N G

g- 1, 1972 L. ANSELRODE 3,631,203

METHOD FOR MANUFACTURING A METAL STENCIL I Filed Oct. 23, 1970 INVENTORI! fi -L I ATTORNEYS United States Patent 4 Int. Cl. B41c 1/14; C231)7/00 U.S. Cl. 204-11 4 Claims ABSTRACT OF THE DISCLOSURE Method formanufacturing a metal stencil by starting from a cylindrical metalmatrix having on its surface a pattern of insulating material; a thinmetal wire is tightly wound upon said matrix, after which a layer ofmetal is deposited upon the matrix, whereupon this layer is removed fromthe matrix.

SURVEY OF THE PRIOR ART The invention relates principally to a methodfor manu facturing a metal stencil comprising a perforated first layerand a second layer composed of wires. So far this method was performedby disposing two gauzes over each other which were at firstcylindrieally bent and subsequently secured. The inner cylinder obtainedby soldering or welding, consists of a strong wire netting serving as asupporting cylinder. A finer gauze is tensioned around this lattercylinder. The finer gauze may consist of a flat fabric which ispermanently held in a cylindrical form by means of a glued joint, or thegauze may already previously be embodied as a seamless knittedcylindrical hose.

This known method is advantageous in that for the outer layer a veryfine gauze may be selected. A considerable drawback, however, consistsin that owing to the supporting inner cylinder the squeegee within thestencil cannot come directly in touch with the stencil cylinder properduring the printing operation and consequently the quality of printingis impaired.

It should be observed that still two other methods for manufacturingcylindrical metal fiencils are known. So by a galvanic process metal canbe deposited on a cylindrical matrix bearing a pattern of non-conductivepoints which do not protrude from the surface of the matrix. At thelocation of these points no metal is deposited, but from the edges metalis gradually deposited in the area of the non-conductive screen pointsand as a consequence the diameter of the perforations aimed at decreasesas the thickness of the deposited layer of metal increases.

According to this known process the finest stencil which can bemanufactured thereby is provided with 1600 to 2000 perforations per cm.The diameter of the perforations amounts then only to forty to fiftymicrons at a thickness of wall of about eighty microns.

If it is desired to make a still finer stencil then it is necessary tomanufacture a still thinner screen cylinder. The life time of such astencil is, however, very short owing to the weakness thereof. From thetechnical viewpoint it is therefore not justified in practice to go inthis process beyond 2500 perforations per cm There may yet be pointed toanother method which bears a similarity to the process just described,but whereby the non-conductive screen points are provided on the surfaceof a smooth matrix via a photographic process. Owing to complicationsproduced on sliding such a stencil from the matrix, this method is onlyapplied to the manufacture of a designed stencil of which only one orsome copies are wanted. Moreover on applying the screen pointsphotographically a flat photographic film should be used which onwinding around the cylindrical matrix produces a seam which considerablylimits the applicability of the method.

SUMMARY OF THE INVENTION It is an object of the invention to provide amethod for the manufacture of a stencil with a very fine perforation andwhich has a suflicient strength, and with which stencil a particularlysharp product or printed matter can be obtained. The invention startsfrom the known method mentioned in the opening part of thisspecification.

The aforementioned objects are attained according to the invention:

in that on starts from a matrix with a two-dimensional curve andelectrically conductive surface bearing a pattern of insulatingmaterial;

in that one tightly applies a single row of very fine wires,

spaced from each other, upon this matrix;

in that one deposits metal on the matrix by a galvanic process, so thatthe wire is anchored in the deposited metal layer;

in that the deposited layer is removed from the matrix.

Due to these features an entirely new type of stencil is obtained whichallows for much finer perforations, while the aforementioneddisadvantages are avoided and the squeegee can come very close to theprinting outer surface of the stencil.

The product obtained with the method according to the invention isdistinguished in that the stencil as it were is constructed from twodifferent materials united into a whole, the perforation on the innerside being mostly not identical to that on the outer side Due to thisnew method a screen cylinder or stencil is obtained, having on its innerside a screen corresponding to the matrix While the outer side exhibitsa slotted screen consisting of parallelly extending slots (the spacebetween the juxtaposed wires).

The invention is also based on the understanding that in order to absorbthe forces transverse to the direction of the squeegee it sufiices touse a Wall thickness amounting to 25-33% of that required to absorb thefrictional forces of the squeegee acting perpendicular thereto. Thelatter force to which is added the frictional force exerted by thematerial to be printed upon the stencil is entirely absorbed by thewires. As a result the usual thickness of microns required for galvanicstencils can be reduced to only 25 to 30 microns, whilst maintaining acommensurate strength and life time of the stencil.

A preferred embodiment of the method according to the invention isobtained when one starts from a cylindrical matrix and when the row ofwires is applied by winding helically at least one wire around thematrix. Hereby it is possible to obtain in a very simple way a tightwinding of the wire around the matrix, whereby also a very exact mutualspacing of the consecutive windings can be maintained.

The wire or wires applied according to the invention may have a ratherarbitrary compositions but preferably a wire of conductive material orwith a conductive surface is applied. The embedment is thereby improvedand the progress of the galvanic part of the process is facilitated. Anon-conductive wire will preferably be used when the mechanical load ofthe stencil to be manufactured in the operative direction of thesqueegee is small and when a very high value is attached to the greatestpossible distance between the windings of the wire at a given number ofwindings per cm. of the length of the matrix.

The invention renders it possible on performing the method to start froma matrix provided with a screen consisting of grooves whichsubstantially extend perpendicularly to the curvature of the surface ofthe matrix. The width of these grooves determines then the one dimensionof the perforations aimed at, while the mutual spacing of the wireslying in the close proximity of each other determines the otherdimension.

The invention will be clarified with reference to the accompanyingdrawing in which to a considerably enlarged scale a plan view of a smallpart of the stencil is depicted (FIG. 1) and further a number of crosssections are represented (FIGS. 2 to 6) of the product according to theinvention, and a section (FIG. 7) through a stencil manufacturedaccording to a conventional process, while finally very diagrammaticallyto a strongly reduced scale a device for performing the method accordingto the invention is represented (FIG. 8).

DESCRIPTION OF A PREFERRED EMBODIMENT Upon a cylindrical metal matrix 1a screen of shallow pits or grooves 2 is manufactured by etching or by amechanical process, e.g. by means of a milling roller. These pits orgrooves are filled up by an insulating material e.g. enamel or syntheticresin. FIG. 1 shows a particular embodiment in which these groves 2 havea width of 250 microns and a length of 1000 microns. These grooves areinterspaced b dams with a width of 30 microns. The longitudinal axis ofthe grooves extends parallel to the longitudinal axis of the matrix (seeFIG. 7). Thereupon the metal surface of the cylinder 1 is passivatedaccording to a known galvanotechnical method in such a way that a metalsubsequently deposited thereon by a galvanic process does not adherethereto.

Thereupon a single row of very thin mutually spaced wires 3 are providedtight on the matrix 1 by means of a winding device 6 which isdiagrammatically represented in FIG. 7. In the situation depicted inFIG. 1 the wire has a diameter of fifty microns and the spacing amountsto hundred microns. Consequently there are odd sixty six windings percm. length of the matrix. When the beginning and the end of the wire 3have been fastened to the matrix 1, the matrix is introduced into agalvanic bath e.g. a nickel bath. By a galvanic process a layer 4 ofnickel of 30 microns in thickness is formed on the matrix, this layerenclosnig the windings of the wire entirely. This enclosure is promotedby the deposition upon the wire itself of a layer of nickel of aboutthirty microns.

The final shape of the stencil is represented in FIG. 1 and inlongitudinal sections according to the lines IIII and I-II'III (seeFIGS. 2 and 3) and in a cross section according to the line IVIV (seeFIG. 4). The total wall thickness of the screen cylinder obtained is noweighty microns. The permeability compares favourably with that whichwould be obtained when by the conventional galvanic method a screencylinder with a wall thickness of eighty microns would be manufactured.In the production of stencils according to the invention the inevitableaccretion of nickel in the lateral direction over the non conductivelocations will only give rise to a decrease of the permeability of thebase screen from 250 microns to a value of 250 minus (2x30)=190 microns.

When starting from FIG. 1 the wire windings are not provided (see FIG.7) and in the nickel bath a screen cylinder is produced of eightymicrons in thickness in order to obtain the required rigidity then thecapacity of the perforations would be decreased to 250 minus (2 X 80):90 microns.

This is evident when FIG. 7 is compared with FIG. 5. Due to thedirection of the grooves 2 parallel to the longitudinal axis of thematrix, the invention renders it possible that the screen cylindermanufactured thereon obtain; at a maximal capacity also a maximalstrength 4 in the direction of the centre line '5, whereby the thicknessof wall can be kept as small as possible.

It should be noted that the application of a cylindrical matrix isfavourable but not essential for the invention. It suffices to use amatrix with a two dimensional curved surface on which a number ofparallel wires are stretched. In that case a flat stencil and nocylindrical stencil is obtained.

It is also favourable but not strictly necessary for the invention toprovide grooves 2 in the surface of the matrix. It is also possible toprovide pits in the surface or grooves along the entire length of thematrix. In the last case the screen cylinder obtained is constituted byslightly flattened wires in the longitudinal direction of the matrix ofthe same form as the cross section according to the line V-V (see FIG.5) and consisting of the galvanically deposited metal on which and inwhich the cylindrical wire windings are anchored.

Finally it should be noted that in the production of flat stencils thestarting point may also be cylindrical matrix, whereby after themanufacture of the stencils the cylinders obtained are severed in thelongitudinal direction.

Summarizing, the advantages of the stencil manufactured whilstperforming the method according to the inveniton can be indicated asfollows:

in spite of the very small thickness of the metal layer deposited by agalvanic process the stencil exhibits a considerable strength especiallyin the direction of the movement of the squeegee;

the stencil is particularly resistant to changes in dimensions since norelative shifting of the crossings of the wires from a woven gauze cantake place;

the consumption of material is considerably limited with respect to theconventional galvanic method.

What I claim is:

1. A method of manufacturing a metal stencil having a perforated firstlayer and a second layer composed of wires, comprising the steps of:

(a) providing a matrix with a two-dimensional curved and electricallyconductive surface bearing a pattern of insulating material;

(b) applying a single row of wires to the matrix over said conductivesurface and said pattern of insulat ing material, said wires beingspaced from each other upon the matrix;

(c) depositing metal on the matrix by a galvanic process so that thewires are anchored in the deposited metal layer; and

(d) removing the layer from the matrix.

2. A method as defined in claim '1 wherein the matrix is cylindrical,and the row of wires is applied by helically winding at least one wirearound the matrix.

3-. A method as defined in claim 1 wherein the wire applied includes aconductive surface.

4. A method as defined in claim 1 wherein the matrix includes a screenhaving grooves which extend perpendicularly with respect to thecurvature of the surface of the matrix.

References Cited UNITED STATES PATENTS 2,246,380 6/1941 Norris 204-412,282,203 5/1942 Norris 204-11 2,287,122 6/ 1942 Norris n t 20492,213,237 9/1940 Brennan et al. l01 127 3,212,169 10/1965 Glaser et al.204-16 3,482,300 12/ 1969 Reinke 101128.4

HOWARD S. WILLIAMS, Primary Examiner T. TUFARIELLO, Assistant ExaminerU.S. Cl. X.R.

